Production of Magnesium Oxalate from Sea Bittern

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PRODUCTION OF MAGNESIUM OXALATE FROM SEA BITTERN

1 2 2 2 Hanem A. Sibak , Shadia A. El-Rafie , Shakinaz A. El-Sherbini1 M. S. Shalaby and Rania Ramadan 1Cairo University Faculty of Engineering, Egypt 2National Research Center, Chemical Engineering and Pilot Plant Department, Egypt 3EL Bohouth St. (former EL Tahrir St.) Dokki- Giza, Egypt E-Mail: [email protected]

ABSTRACT The present study illustrates the details for precipitation of magnesium from Bittern as magnesium oxalate. The target of study is to prepare magnesium oxalate as a precursor for high purity MgO production. Bittern solution is considered as a byproduct in saline, but it is an ore reserve for many useful elements commercially produced at present based on dolomite, sea water. Its rich composition in various elements; especially magnesium salts gives bittern increasing economical concern for different industrial applications. In the present study, the mechanism of magnesium oxalate precipitation from bittern was investigated using oxalic acid. The global reaction kinetics of magnesium oxalate precipitation from seawater was determined using different molar ratios and varied pH (1-6). The effect of temperature on system kinetics was examined at temperatures between 15 to 80 ᵒC. The effect of molar ratio on reaction conversion was investigated from 1:1 to 1:1.8 (magnesium to oxalic acid). The optimized parameters were found to be feasible to produce pure magnesium oxalate with 99% conversion at stoichiometric molar ratio at room temperature with pH=4. The effect of different calcinations temperature was studied from 450 ᵒC to 1100 ᵒC. All necessary instrumentation and chemical analysis needed for final products characterization have been executed including, XRD, XRF, and SEM analysis.

Keywords: magnesium oxalate, precipitation, sea bittern, liquid-liquid reaction.

1. INTRODUCTION construction, in compound and different industries[3]. The future word-wide production of magnesium High purity MgO is particularly utilized in food and metal is projected to increase substantially over the next manufacture of pharmaceutical while Mg(OH)2 is a mainly decade and beyond, basically as a response to the component in the manufacture of flame retarding perceived requirement to reduce the on-street weight of a reagents[6]. Magnesium is found in minerals such as scope of vehicles as a major way in which fuel dolomite, magnesite, serpentinite, brucite, etc. It is the consumption can be improved with a simultaneous most part recovered from seawater, saline solutions and reduction in the generation of greenhouse gases. bitterns. Sea water contains about 1.3 g/L while the asset Magnesium is one of light metals having a density of 1783 of magnesium-bearing saline around the global is kg/m3. This is 66% of aluminum and one sixth of steel. evaluated to be in the billions of tones [7]. High contents The strength to weight proportion of metal is 158 kNm/kg, of magnesium have been found in salar brines located in which is higher than 130 kNm/kg for immaculate South America[8]and other salt lakes around the world. aluminum. Magnesium metal of high quality when The production of magnesium is technically challenging, compared to its weight proportion, these phenomena as well as having relatively high capital and operating drives a focusing interest to this metal. The business costs. In their simplest form, the two principal methods of required for magnesium according to ASTM B92 (2007) producing magnesium metal involve (a) high-temperature for 9980A is at least 99.80 wt% Mg with impurities, for reduction of magnesium oxide and (b) electrolysis of example Fe, Si, Al and Ca below 0.05wt% each [1]. The molten magnesium chloride. Both options are metal has various industrial uses, for example, magnesium characterized by having high energy requirements [9]. compounds are widely used in the automobiles industry Alternative technologies have been studied such as [2], an alloying component in aluminum alloys (41%), die Cabothermic process, Magnethermic process and SOM casting (32%), steel desulphurization (13%), and different process. In previous study[8] two processes were proposed applications as an industrial chemical (14%) [3]. to remove Mg from the bittern by precipitation using Aluminum industry uses magnesium as alloying to sodium hydroxide and ammonium hydroxide solution. improve the ductility, strength and consumption resistance Such a step produces a mixture of Mg(OH)2and some of aluminum combinations [4]. Magnesium’s use in both impurities which requires further processing to recover aluminum and steel production strongly links its demand valuable Mg metal. The high level of Ca in the brine to these two other metal commodities. The use of would contaminate the Mg products if not removed first. magnesium has generally been constrained by moderately In this work, it was required, to recover highly high cost of production and related energy costs. There pure magnesium oxide from bittern through magnesium have likewise been logical issues around alloy oxalate optimization process. The study was carried out improvement, specifically, expanding creep resistance for experimentally in lab scale. The effect of different drive train applications and enhancing corrosion parameters on Mg oxalate precipitation were studied. The resistance. [5]. Magnesium and its salts have been utilized parameters varied included MR, pH and reaction in many applications for example, agriculture, insulation,

www.arpnjournals.com temperature. The parameters should result highly pure Mg 14ᵒBé) and calcium carbonate and bicarbonate will be oxalate which in turn results in pure MgO. precipitated. In the third stage sea water reached (14- 18ᵒBé) calcium sulfate dehydrate will be precipitated. In 2. MATERIALS AND METHODS the fourth stage sea water converted to mother liquor at (18-24ᵒBé) and Gypsum will be precipitated and sodium 2.1 Materials chloride starting to precipitate. Bittern(100 L) having density of about 1.3325 g/ cm3 (36 °Be) was obtained from EMSC, Egypt (received b) Precipitation ponds: May, 2014),the raw material used in this work is known as Precipitation ponds are consisted of 28 ponds the richest source of Mg2+ ions containing > 85 g/L where all sodium chloride had been precipitated at 24- magnesium. 29ᵒBé (the desired product for the saline company) and Starting with Sea Water of 3.5◦Be and passes residual solution went to drainage ponds. through many stages to reach 36◦Be during the evaporation process as shown in figure (2) as follows: c) Drainage ponds: These ponds consisted of two ponds where the a) Concentration ponds bittern will be concentrated at (30-36°Bé) this bittern full The concentration ponds are consisted of four of magnesium salts. The main chemical composition of stages shown in Figure-1 where in the first stage at bittern was analyzed by atomic adsorption and concentration (3.5-8ᵒBé) organic matter will be reproducibility of bittern by complex metric titration precipitated. In the second stage the sea water reached (8- method as shown in Table-1.

Table-1. Main chemical composition of bittern.

++ ++ -- Composition Mg Ca pH SO4 TDS Conductivity 85.7 0.12 56.9 449533 513 mS/cm,at Bittern(36°Be) 6.24 g/L g/L g/L ppm 25°C

Figure-1. Stages of bittern preparation.

2.2 Chemicals Rasayan Co., with a molecular weight of 53.49, purity 99.0%. for analysis. Calcium carbonate was supplied from 2.2.1 Purchased chemicals EL NASR Pharmaceutical Chemicals Co., not less than From Fluka Chemika company, 99% purity and dried for 4 hr at 105◦C before use. ᵒ C2H2O4.2H2O,oxalic acid Mwt126 g/mol, mp 100-102 C, Assay≥99.0% were supplied, commercial sodium 2.2.2 Prepared reagent hydroxide, NaOH, Mwt= 40 was also used. Hydrochloric All reagents and indicators were prepared acid and Ammonia solution25%, Pure reagent were according to method No. 2340 C and 3500Ca D[95], supplied from ADWIC Co., Assay30-34%. Magnesium calcium Standard solution (0.01022M): method No.2340as sulfate (Heptahydrate) MgSO4.7H2O, was supplied from stated in (Standard Methods for The Examination of Water EL NASR PHARMACEUTICAL CHEMICALS Co., and Waste Water). EDTA (0.1M): method assay 99%. Ammonium chloride, finely supplied from No.2340,Ethylenediamintetraacetic Acid Disodium salt 2-

www.arpnjournals.com hydrate C10H14N2Na2O8.2H2O Mwt=327, Assay≥99.0% a) one liter three-neck round flask, acts as reactor. and is prepared by dissolving 3.7 gm (dried for 2 hrs at 80◦C before use) in 1 liter volumetric flask and diluted to b) Water –cooled vertical reflux condenser. the mark with distilled water and stored in a polyethylene bottle. c) Electrically hot plate and magnetic stirrer to allow heating and agitation of reaction mixture. 2.3. Methods Figure-2 shows the experimental set-up for d) Digital thermometer, (5) Digital pH meter, (6) preparation of magnesium oxalate and consists of: Vacuum filtration pump, (7) Buchner flask.

Figure-2. Laboratory set-up of magnesium oxalate preparation.

2.3.1 Description of the laboratory experiment evaluate the unreacted magnesium in the residual Batch experiments were carried out in one liters solution. three-neck round bottom flask, one side connected to reflux condenser, the second side opening for inserting pH 3. RESULTS AND DISCUSSIONS and temperature probes and the third side opening for sample withdrawal intervals. The 3-necked flask is filled 3.1 Effect of different parameters on reaction with calculated volume of bittern, a Known amount of conversion oxalic acid as precipitant. Sodium hydroxide was used to The effect of different parameters such as adjust pH of reaction. reactant molar ratio, pH and temperature were studied on The precipitation of magnesium oxide from the reaction conversion of oxalic acid at different time bittern was carried out using different precipitants such as interval as follows: oxalic acid, ammonia solution and sodium hydroxide. 3.1.1 Effect of reactants molar ratio (MR) 2.3.2 Precipitation using oxalic acid The molar ratio of the reactants (magnesium to 100 ml of bittern in each experiment at different oxalic acid) greatly influences the rate of batch process. reaction temperature (15 to 80ᵒC), Hot plate was set at To reach the optimum magnesium to oxalic acid molar constant stirring rate of 210 rpm. to homogenize the ratio, the reaction was carried out at fixed temperature solution. Oxalic acid is added to the stirred solution and 25C, pH=4 and different RMR (1:1, 1:1.2, 1:1.4, 1:1.6 6.25M NaOH was continuously added for controlling pH. and 1:1.8). For each molar ratio the magnesium (10 ml) samples were taken at interval time to evaluate conversion was calculated and plotted versus time and full state of reaction. The total amount of sodium hydroxide product characterization was fulfilled for precipitated added was measured through reaction to calculate the solids as XRD, XRF, and SEM. molar ratio of NaOH used with respect to Mg ions in bittern and Oxalic acid in reaction media. After reaction 3.1.2 Effect of pH completion, the precipitate was by a vacuum filtration. Effect of pH was studied at constant MR (1:1) Further the solid was washed with distilled water and constant reaction temperature at 25C. Different pH followed by ethanol. The final precipitate (magnesium was used (1, 3, 4 and 6). Magnesium conversion oxalate) was dried at 100 ºC for 2 hr before analysis. It percentage was plotted versus time and subjected to XRD, was also calcined at 650ºC for 2 hrs. The products were XRF, and SEM analysis. subjected to XRD analysis. EDTA titration was used to

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3.1.3 Effect of temperature conversion was detected at 25C. The batch process was Influence of temperature on each batch process carried out at MR=1:1, pH=4. The reaction conversion was studied at various temperatures 15, 25, 60, and 80C calculated was plotted versus time Figure (3) and Table as. The optimum temperature that provides the highest (2).

Figure-3. Effect of reaction conversion at different time, temperature, MR=1:1 and pH=4.

Table-2. Effect of reaction temperature on magnesium oxalate purity.

Element 15 ˚C 25 ˚C 60 ˚C 80 ˚C % C 18.36 20.86 22.81 32.75 % O 61.43 63.55 61.49 54.26 % Na 5.07 0.78 0 2.68 % Mg 14.47 13.57 13.11 7.98 % Al 0.34 0.82 1.5 0 % K 0 0.41 0 0 % Cl 0.33 0 0 2.33

3.2 Instrumentation analysis 3.2.2. Figure-4 illustrates the XRD patterns of 3.2.1 The content of magnesium in residual magnesium oxalate under this condition, where all peaks solution was determined by Complexometric titration in the pattern could be clearly indexed on the basis of a method using murexide indicator and NaOH to adjust pH monoclinic cell reported for magnesium oxalate. up to 12 as mentioned before.

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●

Figure-4. XRD patterns of Mg oxalate product.

Reaction time is one of the most important shown in Figure-5. Results have shown that all magnesium factors that affect precipitation of magnesium oxalate. At concentration profiles seem to be close at constant molar the end of reaction, most magnesium ions were converted ratio and temperature. Equilibrium was reached within the to pure magnesium oxalate. Complete specification of first 90 min. The removal of bittern containing magnesium product was confirmed by XRD pattern. ions as magnesium oxalate with highest conversion during 2 hours with conversion of 90-98%. Above pH=4, 3.2.3 Effect of pH on reaction conversion magnesium oxalate decomposes to magnesium hydroxide. The influence of pH on the precipitation of magnesium oxalate at MR 1:1 at ambient temperature is

Figure-5. Conversion of magnesium at MR 1:1 to 1:1.8 , temperature (25 °C) and pH= 4.

3.2.4 SEM and EDX analysis of magnesium oxalate precipitated. Not only magnesium oxalate precipitated, The morphology of magnesium oxalate is shown but also sodium and chlorine were present too. EDX at 80˚C as shown in Figure-6a to Figure-6h. EDX analysis shows that main peaks are of magnesium oxalate at these temperatures shows percentage of all elements indicating pure precipitation.

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Figure-6b. EDX of Mg oxalate prepared at 15˚. Figure-6a. SEM of Mg oxalate prepared at 15˚C

Figure-6c. SEM of Mg oxalate prepared at 25˚C Figure-6d. EDX of Mg oxalate prepared at 25˚C.

Figure-6e. SEM of Mg oxalate prepared at 60 ˚C. Figure-6f. EDX of Mg oxalate prepared at60 ˚C.

The purity of magnesium oxalate was calculated P2O -- 0.002 from the above charts at different reaction temperature. It was obvious from Table-3 highest purity of magnesium SO3 0.02 0.02 oxalate was fulfilled at 25 ᵒC. Cl 0.03 0.02

LOI 72.56 73.48 Table-3. XRF Data for before and after washing magnesium oxalate salts. CuO 0.001 --

Before After NiO 0.002 0.002 Concentration of washing (wt, washing (wt, main constituents ZnO 0.002 -- %) %)

SiO3 0.06 0.08 From Table-3 magnesium oxide is stable and is

AL2O3 0.04 0.04 more purified when washed with water as some oxides decreased by washing indicating its dissolution in water. Fe2O3 0.002 -- MgO 26.36 25.45 3.2.5 Effect of calcinations temperature on magnesium oxalate CaO 0.05 0.05 The different calcination temperatures were Na2O 0.39 0.37 studied for magnesium oxalate to optimize magnesium oxide salts for maximum conversion. Products under study K2O 0.5 0.48 were subjected to SEM and EDX tests. The tests of MgO

www.arpnjournals.com powder obtained at different calcinations temperatures were carried out at (500 °C, 650 °C and 1100 °C). The results are shown in Figure-7.a, Figure-7b, Figure-7c, Figure-7d, Figure-7e and Figure-7f. The best calcinations temperature detected is 650 °C to produce high purity MgO. The morphology of MgO was more regular at calcinations temperature of 1100 ºC as shown in Figure- 7g. The percentage of the elements associated with magnesium oxide at different calcinations temperatures was explained in the following Tables (4), (5) ,(6) and (7).

Figure-7c. SEM of MgO calcined at 650 ◦C.

Figure-7a. SEM of MgO prepared at 450 ˚C.

Figure-7d. EDX of MgO prepared at 650 ◦C.

Table-5. Composition of MgO calcined at 650 ◦C.

Weight Atomic Net Error Element % % Int. % 1231.1 Mg 59.48 49.53 4.83 Figure-7b. EDX of MgO prepared at 450 ˚C. 8 Cl 0.68 0.39 11.36 24.84 Table-4. Composition of MgO calcined at 450 ◦C. K 0.44 0.23 6.77 37.64 Weight Atomic Net Error Element Oxygen 39.4 49.85 0 0 % % Int. %

C 13.53 19.23 69.46 11.48 Na 1.36 1.01 35.67 11.98 1345.6 Mg 28.46 19.99 6.07 4 Cl 0.67 0.32 35.05 11.94 K 0.48 0.21 22.25 13.77 Oxygen 55.5 59.23 0 0

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Figure-7e. SEM of MgO calcined at 1100◦C. Figure-7f. SEM of MgO calcined at 1100◦C.

Table-6. Composition of MgO calcined at 1100◦C.

Weight Atomic Net Error Element % % Int. % O 37.72 47.93 333.73 7.29 1344.1 Mg 62.28 52.07 4.64 4

Percentage of loss in weight of magnesium oxalate after burning at different temperatures is shown in Table-7.

Table-7. Percentage weight loss before and after calcination.

Calcination Weight before Weight after % Weight loss %Purity temperature(ºC) calcination (g) calcination (g) 450 5 1.412 71.76 % 83.96 650 5 1.394 72.12 % 98.88 1100 5 1.385 72.3 % 99

4. CONCLUSIONS REFERENCES It can be concluded that the best optimum operating conditions for precipitating pure magnesium [1] Wulandari W., Geoffrey A.B., Muhammad A. R. and oxalate are confirmed at MR=1:1, pH=4, ambient Brian J. M. 2010. Magnesium: Current and alternative temperature and time of reaction for 2 hr. The yield was production route. Chemeca, Engineering at the Edge; 51.662 g with conversion 98.7%. The observed high yield 26-29 September 2010, Hilton Adelaide, South and conversion data were due to using purified Australia. Barton, A.C.T.: Engineers Australia. pp. concentrated bittern solution of 36 Baume′. No other peaks were detected in the spectrum within the 347-357. detection limit of the X-ray diffraction instrument, indicating the purity of the synthesize powder. [2] Mordike B.L. and Eber T. 2001. Magnesium. Properties - Applications - Potential. Materials ACKNOWLEDGEMENT Science and Engineering A. A302(1): 37-45. Our work was supported by the National Research Centre, Chemical Engineering Department and [3] USGS. 2007. Annual Yearbook Magnesium. [Online]. El Max Saline Company in Alexandria. The authors Available: thanks the team colleagues in Cairo University and http://minerals.usgs.gov/minerals/pubs/commodity/ma assistance with XRD, SEM, and XRF studies. gnesium/myb1-mgmet.pdf.

[4] Slade S. 2010. Magnesium: Bridging Diverse Metal Markets. Magnesium Technology, TMS (The Minerals, Metals & Materials Society). pp. 91-95.

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[5] Zang J.C. and Ding W. 2001. The Pidgeon Process in China and Its Future. Magnesium technology, Warrendale, PA, TMS. pp. 7-10.

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[8] An J.W., Kang D.J., Tran K.T., Kim M.J., Lim T. and Tran T. 2012. Recovery of lithium from Uyuni salar brine. Hydrometallurgy. 30: 117-118, 64-70.

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